Author Topic: Anything I should know about 78 CB750k before I get one? (Read 3098 times)

greenjeans · « **on:** February 04, 2019, 09:14:05 AM »

Got a line on a 78 CB750K. Anything quirky about those motors/carbs etc.?

seanbarney41 · « **Reply #1 on:** February 04, 2019, 09:38:00 AM »

Yeah, the carbs are more difficult to rebuild...and they are kinda ugly....but then you already knew that. Better transmission and the engine makes decent power

lrutt · « **Reply #2 on:** February 04, 2019, 10:45:01 AM »

Carbs have accel pumps, that's a good thing, tanks are ugly though, and they have 630 chains. Not worth as much as pre-77's but nothing wrong with them either.

seanbarney41 · « **Reply #3 on:** February 04, 2019, 11:40:19 AM »

Also...if you need carb boots, and you probably will, repro are as much as oem early boots, but inferior quality and oem are nla....some other parts can be tough to source....like petcocks.

kerryb · « **Reply #4 on:** February 04, 2019, 11:51:48 AM »

Those were my first carb rebuild. Worked out fine, total dissaembly, clean and reassemble. Hardest part was learning tricks to get boots off and on. Great bike

BenelliSEI · « **Reply #5 on:** February 04, 2019, 01:32:34 PM »

Great motorcycle! Tons of value/$! I’ve restored a K7 and a K8. It’s true that a few parts are slightly harder to source because that are unique to the models. Rear rim springs to mind (it’s 17”). On one of the K8’s we just used an 18” and the correct spokes, no issues.

kerryb · « **Reply #6 on:** February 04, 2019, 02:52:27 PM »

Quote from: BenelliSEI on February 04, 2019, 01:32:34 PM

Great motorcycle! Tons of value/$! I’ve restored a K7 and a K8. It’s true that a few parts are slightly harder to source because that are unique to the models. Rear rim springs to mind (it’s 17”). On one of the K8’s we just used an 18” and the correct spokes, no issues.

Whoa! Good lookin bikes...wish mine looked that good.

Gregorymoto · « **Reply #7 on:** February 04, 2019, 05:29:22 PM »

Nope!!

madmtnmotors · « **Reply #8 on:** February 04, 2019, 05:48:15 PM »

K8's are the fastest!

HondaMan · « **Reply #9 on:** February 04, 2019, 05:52:07 PM »

They are cold-blooded, compared to the earlier ones: you can install a #37.5 or #40 pilot jet and overcome this, easily. Use genuine Keihin parts when you do, and it will be great.

The K7/8 engines used cast iron valve guides, and many of them have worn out their exhaust guides badly at relatively low miles. Bronze guides, like the ones from APE, will fix this right up, and forever. The symptom: oil weeping out the front, near the pipe headers.

Other than these things, the K7/8 are as fine a bike as any CB750!

sixthwisconsin · « **Reply #10 on:** February 04, 2019, 07:05:41 PM »

PD carbs are beautiful!!

Can550 · « **Reply #11 on:** February 04, 2019, 09:00:04 PM »

I loved mine as long as I had it. Sold in October last year. Rode it 3,000 kms.

Bought it at 8,100kms
Sold at 11,100 kms

New owner loves it, great bikes

Sent from my iPhone using Tapatalk

greenjeans · « **Reply #12 on:** February 05, 2019, 12:27:53 PM »

Quote from: HondaMan on February 04, 2019, 05:52:07 PM

They are cold-blooded, compared to the earlier ones: you can install a #37.5 or #40 pilot jet and overcome this, easily. Use genuine Keihin parts when you do, and it will be great.

The K7/8 engines used cast iron valve guides, and many of them have worn out their exhaust guides badly at relatively low miles. Bronze guides, like the ones from APE, will fix this right up, and forever. The symptom: oil weeping out the front, near the pipe headers.

Other than these things, the K7/8 are as fine a bike as any CB750!

That's what I was trying to remember. How easy is it to remove and replace the guides? Any tips?

flybox1 · « **Reply #13 on:** February 05, 2019, 01:22:46 PM »

guides are easy to remove with a guide punch. Just a few whacks is all mine took.

HondaMan · « **Reply #14 on:** February 05, 2019, 07:18:06 PM »

Once the guides are changed, the seats must be recut to match. The angle of the guides changes slightly when the guides are removed and installed, and when the clearances are correct, the valves usually will not seal afterward. Don't be tempted to simply increase the guide-stem clearance to "fix" this, or you will be right back where you started: I get quite a few heads this way...use bronze guides, like APE or Kibblewhite, and bare-minimum guide-stem clearances: you will LOVE the results.

beemerbum · « **Reply #15 on:** February 06, 2019, 02:02:50 PM »

Quote from: greenjeans on February 04, 2019, 09:14:05 AM

Got a line on a 78 CB750K. Anything quirky about those motors/carbs etc.?

The 77 and 78 K bikes seem more substantial as you ride them. Earlier 750K's seem smaller because they are. I believe the later wheelbase is longer. Contrary to many folks here, I thought the 77/78 exhausts are better looking than the earlier pipes. I would have kept them, however they were so rusted out I could hear pieces of baffles rattling around inside. Repops are available from DSS at about $700 plus shipping. My '77 has responded very well to a 4 into 1 from Delkevic. Of all my SOHC4's my '77 is my favorite ride.

bamacb · « **Reply #16 on:** February 14, 2019, 08:44:27 AM »

Quote from: HondaMan on February 04, 2019, 05:52:07 PM

They are cold-blooded, compared to the earlier ones: you can install a #37.5 or #40 pilot jet and overcome this, easily. Use genuine Keihin parts when you do, and it will be great.

The K7/8 engines used cast iron valve guides, and many of them have worn out their exhaust guides badly at relatively low miles. Bronze guides, like the ones from APE, will fix this right up, and forever. The symptom: oil weeping out the front, near the pipe headers.

Other than these things, the K7/8 are as fine a bike as any CB750!

I have two of these heads and the exhaust guides are about as bad as I've ever seen. The intakes check out good but what is the thought on replacing them also or do they tend to last ?

Xander^ · « **Reply #17 on:** February 14, 2019, 09:45:08 AM »

how do i find new gold gas tank emblems, or whats the best was to get my original ones gold again.. they were all roughed down and sanded ...

BenelliSEI · « **Reply #18 on:** February 25, 2019, 11:37:38 AM »

For new tank and side cover graphics, check out AFEGRAPHICS.COM I’ve mentioned this site before. The fellow is a few miles from me and does amazing work. His stuff sells through many of the sites we regularly use, try dealing direct! You won’t see any Honda decals listed because HONDA goes after manufacturers selling unlicensed product (even though they don’t sell these). But if you look through his GALLARY photos, you will find every style of SOHC CB750, including K7 and K8. Just send him and email enquire for availability and pricing.

HondaMan · « **Reply #19 on:** February 28, 2019, 05:01:43 PM »

Quote from: BenelliSEI on February 25, 2019, 11:37:38 AM

For new tank and side cover graphics, check out AFEGRAPHICS.COM I’ve mentioned this site before. The fellow is a few miles from me and does amazing work. His stuff sells through many of the sites we regularly use, try dealing direct! You won’t see any Honda decals listed because HONDA goes after manufacturers selling unlicensed product (even though they don’t sell these). But if you look through his GALLARY photos, you will find every style of SOHC CB750, including K7 and K8. Just send him and email enquire for availability and pricing.

+1 on AFE graphics: when I restored my K7 I used them, and I think they sold the bike instantly when the [prospective] new owner first saw it.

SierraCB · « **Reply #20 on:** February 28, 2019, 06:30:29 PM »

+1 to most of everything said here. I will double up with the bike being fairly cold blooded. Mine needs a pretty decent amount of time to act normal with a lot of choke modulation... Once warm it's perfect though.

Don R · « **Reply #21 on:** March 04, 2019, 09:01:51 PM »

Quote from: beemerbum on February 06, 2019, 02:02:50 PM

Quote from: greenjeans on February 04, 2019, 09:14:05 AM
Got a line on a 78 CB750K. Anything quirky about those motors/carbs etc.?
The 77 and 78 K bikes seem more substantial as you ride them. Earlier 750K's seem smaller because they are. I believe the later wheelbase is longer. Contrary to many folks here, I thought the 77/78 exhausts are better looking than the earlier pipes. I would have kept them, however they were so rusted out I could hear pieces of baffles rattling around inside. Repops are available from DSS at about $700 plus shipping. My '77 has responded very well to a 4 into 1 from Delkevic. Of all my SOHC4's my '77 is my favorite ride.

I agree, my 77K and 76 F also seemed to be bigger bikes than my older ones. I believe it's the frame length and fork offset combined.

BenelliSEI · « **Reply #22 on:** March 05, 2019, 05:21:14 AM »

I agree about the pipes...... really great looking. Like the tank, and seat, they added to the “bulking up” of the motorcycle. I bought my K7 because it appeared under valued compared to the earlier years. Great machine and 25 years later, I still have it!

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Author Topic: Anything I should know about 78 CB750k before I get one? (Read 3098 times)